MYSTERY still surrounds the reason why swimmers fell ill after swimming in the sea off north Essex.

Hundreds of families were enjoying the sun in Clacton, Frinton and Walton on the hottest late August bank holiday weekend on record when a large number of people began to have trouble breathing.

So here is what we know as thousands of people are set to head to the coast today.

Emergency services called to reports of swimmers falling ill

Emergency services, including the ambulance and fire service, were called to the seafront off Fourth Avenue shortly after 2pm on Sunday.

A "small" number of people were taken to hospital for further evaluation, in a stable and non-life-threatening condition.

Visitors to the beaches reported struggling to breathe, coughing and feeling unwell.

An investigation is underway

Essex Police is investigating, but the cause remains unknown.

A spokesman said: "The cause for this is currently unknown and we and our partner agencies are working to try and establish the cause as quickly as possible.

"While we are doing this, we are advising people to not go into the sea."

Despite speculation of a fuel spill from a ship, the Maritime and Coastguard Agency, which sent a counter surveillance pollution aircraft to the scene, said no evidence of this has been found.

A spokeswoman for the Maritime and Coastguard Agency said: "At around 2.30pm on Sunday afternoon, HM Coastguard received reports of beach swimmers suffering from a possible respiratory irritant causing people to cough at Frinton and Walton.

"The Maritime and Coastguard Agency has not received any reports of pollution being spilled in the area from vessels.

"The MCA's counter pollution surveillance aircraft has flown over the area this afternoon to undertake an aerial survey and no fuel pollution has been reported by this flight."

What is the advice to people who have been in the sea

East of England Ambulance Service said people should wash themselves down if they were in the water, change their clothes and drink fresh water.

Anyone with further concerns is advised to call the NHS on 111.

A spokesman for the ambulance service added: "We are aware of an incident on Sunday with reports of a number of people suffering from coughing on the seafront off Fourth Avenue, Frinton.

"We are assisting the police and fire services with this incident.

"The cause is currently unknown."

People are being advised not to go in the sea while the investigation takes place.

Tendring Council: 'No reason to be alarmed'

Alex Porter, cabinet member for leisure and tourism, said there was no reason for people to be alarmed.

“No-one has been seriously hurt, and while work is ongoing to establish the cause it would be unwise to speculate,” he said.

“Pending the outcome of that work, current advice is to avoid going into the water, and we would encourage people to respect that.

"Our Beach Patrol teams, which will be increased on Bank Holiday Monday, will continue to advise beach goers and keep them up to date.

“There is much more to our coastline than just the sea though – we have beautiful, award-winning beaches, lovely promenades just right for a stroll in the sunshine, and glorious seafront gardens and parks just right for enjoying the sunshine.

“Coupled with numerous businesses selling cold drinks and ice creams to help visitors beat the heat, Clacton, Frinton and Walton remain good places to visit for Bank Holiday Monday.”

Tendring Council added that it is part of the multi-agency response looking to establish what the cause of the symptoms were.

Clacton MP Giles Watling said: “I’ve been in touch with the Home Secretary and we are jointly looking into the details of what has happened.

“At this stage establishing the facts and ensuring that people who need support are being assisted is our priority.

“Priti Patel spent a day in Frinton last week and had a fabulous day.

“We need to return to normal as soon as possible.

“I have spoken to local residents who are still enjoying this great weather on our wonderful coastline.”